1. Field of the Invention
The present invention relates to the field of optical telecommunication networks, and more specifically to duplexers, that is, terminals capable of receiving an optical signal at a first wavelength and of transmitting back in controlled fashion optical signals at a second optical wavelength.
Such devices are for example used in telecommunication networks to receive, at the level of a subscriber terminal, a communication from a server via an optical fiber and to send adapted response signals to the optical fiber towards the server.
2. Discussion of the Related Art
As illustrated in FIG. 1, such duplexers have initially been formed by means of discrete components. An optical signal at a first optical wavelength λ1, for example, 1.5 μm, is sent by an optical fiber 1 towards a subscriber terminal 2. The subscriber terminal comprises a splitter sending back the signal at the first optical wavelength to a receiver (REC) 4. The subscriber terminal also comprises an emitter (EM) 5, that may be controlled by an electronic control circuit 6, connected to receiver 4 to send back into the optical fiber, through splitter 3, a beam at a second optical wavelength λ2, for example 1.3 μm.
As optical, microphotonic, and now nanophotonic integrated circuits have been developing, it has been attempted to form the entire data terminal 2 in the form of a monolithic integrated optical component. Various problems of coupling between the signal originating from the optical fiber and the receiver, and of coupling of the beam transmitted back to the optical fiber are then posed. Further, a crosstalk issue is raised, that is, there is a risk for a portion at least of the retransmitted beam to be sent to the receiver, thus disturbing the indications thereof.
Various integrated optical circuits have been provided in prior art and are mostly based on polarization splitting systems. However, such systems have a very poor efficiency. Generally, they have a coupling efficiency between an incident beam and a transmitted beam which is hardly greater than 20%.
Efficient duplexers made in the form of optical integrated circuits are thus needed.